The invention relates to improvements in flexure-resistant pressure rolls for use in calenders and like machines. More particularly, the invention relates to improvements in rolls of the type disclosed in commonly owned U.S. Pat. Nos. 4,520,723 (granted June 4, 1985 to Pav et al.), 4,394,793 (granted July 26, 1983 to Pav et al.), 4,328,744 (granted May 11, 1982 to Pav et al.) and 4,457,057 (granted July 3, 1984 to Pav).
It is known to assemble a flexure-resistant roll for use in roll stacks of machine calenders, supercalenders and press sections from a cylindrical shell and a stationary shaft or an analogous carrier which is spacedly surrounded by the shell. The shell has a certain freedom of radial movement relative to the carrier, and its shape is controlled by one or more rows of hydrostatic bearing elements which are interposed between the shell and the carrier and are operated in response to signals from sensors which monitor the quality of the processed web, the temperature of the peripheral surface of the shell and/or other parameters. Such regulation of the shape of the shell is necessary in order to influence the geometry of the nip between the shell and an adjacent roll. It is further known to provide the ends of the shell with sleeves which are surrounded by bearings and are movable radially of the shell, at least in a plane which includes the nip and the axis of the shell, so as to allow for a widening or narrowing of the nip in directions which are parallel to the supporting plane of the roll.
A roll wherein the bearings at the ends of the shell are movable radially of the carrier is marketed by the assignee of the present application under the designation "HYDREIN Typ R". This roll has several rows of hydrostatic bearing elements and its shell is free to float in the radial direction relative to the carrier. Such arrangement is desirable and advantageous because it eliminates the need for external roll loading. The bearings at the ends of the shell surround sleeves having a predetermined freedom of radial movement in directions which are parallel to the supporting plane of the roll. Reference may also be had to German Pat. No. 31 24 616, to German Auslegeschrift No. 28 26 316, and to German Offenlegungsschrift No. 31 38 365.
Another roll which is manufactured by the assignee of the present application and is known as "HYDREIN Typ C" is constructed and assembled in such a way that the bearings at the axial ends of the shell are mounted directly on the stationary carrier, i.e., the end portions of the shell cannot float relative to the carrier. The mode of operation of hydrostatic bearing elements which are interposed between the shell and the carrier is the same as in the "HYDREIN Typ R" roll.
The just discussed rolls can be used in a wide variety of machines. One of the presently preferred uses of such rolls is in the paper processing industries. Certain other types of supercalenders employ both types of rolls, i.e., those wherein the shell can float radially of the carrier and those wherein the end portions of the shell can rotate relative to but cannot move radially of the carrier. The presence of two types of rolls renders it necessary to maintain two sets of spare parts. Moreover, and since such rolls are often used in mass-producing plants, it is necessary to maintain at least one roll of each type in a state of readiness for immediate replacement of a defective roll. All this contributes to initial and maintenance cost of the machines as well as to space requirements for spare parts and spare rolls.